1. Field of Invention
The present invention generally relates to a material handling device and, more particularly, to a vacuum friction feeder.
2. Description of Related Art
Bottom-feeding friction feeders are used to individually remove flat stock from the bottom side of a stack and sequentially feed the flat stock into another device such as, for example, a printer, a labeler, a dryer, a collator, a folder or an inserter. Conventionally, the stack of flat stock is positioned such that a portion of the bottom sheet is exposed at an angle to one or more rotating rubber belts. By adjusting factors such as the angle of the stack relative to the belts (which is also known as the “wedge”), the speed of the belts etc., it is possible to sequentially draw a sheet of flat stock from the stack and separately feed the sheet into another device or a conveyor.
One of the problems that exists with conventional friction feeders is that it is often difficult, if not impossible, to feed different types of flat stock (e.g., flat stock which is thick, or rigid, or wide, or limp etc.) using the same friction feeder. Conventional devices have a difficult time feeding long, wide, dense flat stock (e.g., 36″×16″ paper feed bags). In such applications, it is difficult to make appropriate adjustments to the “wedge” to expose an optimal amount of the material to the belts. Therefore, it is difficult to obtain enough control over the amount of exposure, particularly with longer products, to consistently feed product one at a time (i.e., without feeding multiple pieces at a time).
Another problem with feeding dense (heavy) material is the amount of material that may be loaded into the stack or “hopper”. The angled design of conventional devices limits the amount of material that can be loaded into the hopper. Furthermore, testing has shown that in conventional friction feeders, as the amount of material remaining in the hopper changes (i.e., decreases over time), the belt exposure wedge conditions change. So as the material is feed and the hopper is depleted the feed characteristic is changed causing feed issues. All these problems make it difficult for the operator to setup and run current device in an effective manner.
Loading various size products is problematic because of the wedge design. Products longer than the feeder have to be supported behind the feeder in order to get any type of consistent feeding. With the conventional wedge design, the height at which the operator has to load the hopper becomes a major issue.
Feeding limp feed stock is also a problem for conventional friction feeders. In such applications, the product exposure wedge has to be set so close to the leading edge that the back of product becomes basically unsupported, which causes problems feeding when any significant amount of product is loaded in the hopper.